site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com On Dec 21, 2006, at 6:55 PM, Bhavesh Davda wrote: So I did this from my iff_output_func callback: mbuf_get_csum_requested(*data, &csumFlags, NULL); if (csumFlags) { ipHdr = (struct iphdr *)((uint8 *)mbuf_data(*data) + ETHER_HDR_LEN); if (ipHdr->tot_len > mbuf_pkthdr_len(*data)) { /* ip_len must be in network-byte-order. Byte-swap it. */ ipHdr->tot_len = ntohs(ipHdr->tot_len); swapIpLen = TRUE; } mbuf_outbound_finalize(*data, PF_INET, ETHER_HDR_LEN); /* byte-swap ip_len back. */ if (swapIpLen) { ipHdr->tot_len = htons(ipHdr->tot_len); } I *think* this is what your suggestion was. This makes the kernel panic! I attached to the kernel and examined the mbuf, and it looked totally messed up. Several pointers were pointing to la-la land, the data in m->m_hdr.mh_data was munged from its original values, etc. The same was the case (messed up mbuf) when I set a breakpoint after mbuf_outbound_finalize() and examined it, on a non-panic'ed kernel. What am I, as poor KEXT author, doing wrong? The i386 version of in_cksum_skip() is too hard for a simple minded person like me to figure out :) Try this instead: static errno_t iff_output(void *cookie, ifnet_t interface, protocol_family_t protocol, mbuf_t *data) { if (protocol == AF_INET) { u_int16_t ip_len; size_t offset = sizeof (struct ether_header) + offsetof(struct ip, ip_len); return (0); } Adi _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... This email sent to site_archiver@lists.apple.com Your filter shouldn't assume that the headers are in a contiguous span; instead, you should probably use mbuf_copydata() to be safe. In addition, your code above compares the result of mbuf_pkthdr_len() against the *network* byte-order value of IP length; the ntohs() part should be done before that check. if (mbuf_copydata(*data, offset, sizeof (ip_len), &ip_len) == 0) { ip_len = ntohs(ip_len); mbuf_copyback(*data, offset, sizeof (ip_len), &ip_len, MBUF_WAITOK); mbuf_outbound_finalize(*data, protocol, sizeof (struct ether_header)); mbuf_copydata(*data, offset, sizeof (ip_len), &ip_len); ip_len = htons(ip_len); mbuf_copyback(*data, offset, sizeof (ip_len), &ip_len, MBUF_WAITOK); } } smime.p7s